This invention relates in general to imaging, and more specifically, to a novel migration imaging system.
There has been recently developed a migration imaging system capable of producing high quality images of high density, continuous tone, and high resolution. This system is described and claimed in application Ser. No. 403,002, filed Oct. 12, 1964, now abandoned, U.S. Pat. No. 3,520,681, and in copending applications Ser. No. 837,780, and Ser. No. 837,591, both filed June 30, 1969, now Pat. Nos. 3,975,195 and 4,013,462, respectively. In a typical embodiment of this imaging system, a migration imaging member comprising a substrate with a layer of softenable or soluble material, containing electrically photosensitive particles overlying the substrate is imaged in the following manner: An electrical latent image is formed on the electrically photosensitive surface, e.g., by uniform electrostatic charging and exposure to a pattern of activating electromagnetic radiation. The softenable layer is then developed by exposing the plate to a solvent which dissolves only the softenable layer. The photosensitive particles which have been exposed to radiation migrate through the softenable layer as it is softened and dissolved, leaving an image on the substrate conforming to a negative of the original. This is known as a positive to negative image. Through the use of various techniques, either positive to positive or positive to negative images may be made depending on the materials used, the charging polarities, and other imaging parameters. Those portions of the photosensitive material which do not migrate to the substrate may be washed away by the solvent with the softenable layer.
In general, three migration imaging members may be used: A layered configuration which comprises a substrate coated with a layer of softenable material, and an overcoating of electrically photosensitive material (usually particulate) contiguous the upper surface of the softenable layer; a binder structure in which the electrically photosensitive particles are dispersed throughout the softenable layer which overcoats a substrate; and an overcoated structure in which a substrate is overcoated with a layer of softenable material followed by an overcoating of electrically photosensitive particles and a second overcoating of softenable material which sandwiches the electrically photosensitive particles.
The migration imaging process comprises a combination of process steps which include charging, exposing and developing. The characteristics of these images are dependent on such process steps as charging potentials, exposure levels, and development techniques, as well as the particular combination of the various process steps. High density, continuous tone and high resolution are some of the photographic characteristics which are possible to achieve in this system. The image is characterized as a fixed or unfixed electrically photosensitive powder image which can be used in a number of applications such as microfilm, hard copy, optical masks, or stripout applications using adhesive materials. Alternative embodiments of the system are further described in the above cited copending applications.
In a related imaging system described in copending U.S. Patent application Ser. No. 483,675, filed Aug. 30, 1965, electrically photosensitively-inert particulate material is used to form images in the migration imaging system already defined above. In this system, a developable image is formed by charging in image configuration through the use of mask or stencil. This latent image is then developed, for example by contacting the member with a solvent for the softenable material.
In another recently developed imaging system, an image is formed by the selective disruption of a particulate material overlying an electrostatically deformable film or layer. The imaging structure used in this system is substantially the same as that used in the imaging system already described above, and involves exposing the charged member to an optical image to selectively relocate the charge and form a developable charge pattern. The softenable layer is then developed or softened by heat whereupon the fracturable or particulate layer is selectively disrupted resulting in a rearrangement of the particles to form an image viewable by reflected or transmitted light. When the structure is developed by heat, the electrically photosensitive area or layer is disrupted and the electrically photosensitive particles are thereby selectively rearranged to change the optical properties of the plate. The image is believed to be formed because the electrically photosensitive particles drift on top of one another and accumulate in valleys or pockets of the deformation image leaving the raised portions of the image uncovered. This imaging system is believed to be substantially due to a surface disruption effect with no substantial migration of the electrically photosensitive particles within the softenable layer. This final image differs from that of the migration imaging system described above, in that the softenable layer is deformed in conjunction with a disruption of the photosensitive particles. This system is described and claimed in application Ser. No. 520,423, filed on Jan. 13, 1966, now abandoned, U.S. Pat. No. 3,542,545.
Although each of the above imaging systems is capable of producing excellent images, there is a continuing need for more simplified systems which provide even higher quality images for example, new systems having high density images and low background.